1. Field of the Invention
The present invention relates to a lapping apparatus and method used in the lapping process for the manufacture of thin film magnetic heads.
2. Description of the Related Art
A magnetic head slider used in a magnetic disc provides at least one thin film head element, which is located at a trailing edge (exhaust side of the air flow) of the magnetic head slider, and a magnetic head slider is provided such that such floats above the surface of the magnetic disc by rotating the magnetic disc.
In the manufacturing process, a plural of magnetic head elements are formed on a wafer (substrate), and the wafer is cut into a plurality of bars, which have a plurality of magnetic head elements in line, and then lapping of the air bearing surface (ABS) of a bar is performed, wherein the air bearing surface comprises the surface which faces the surface of the magnetic disc.
FIGS. 1a and 1b are a plane view of a holding jig, which is used in a lapping method according to the prior art, showing from a lapping plate side.
For the lapping method according to the prior art, as shown in FIGS. 1a and 1b, a triangle shaped holding jig 10 or a square shaped holding jig 11 which can rotate themselves around a supporting point 10a or 11b is used. More specifically, three bars 12 or four bars 13 to be lapped are fixed on the plane 10b or 11b of the holding jig, whereby the plane 10b and 11b face the lapping plate, and the surface to be ABS of the bars 12 or 13 are lapped by rotating the holding jig 10 or 11 around the supporting point 10a or 11b as well as rotating the lapping plate.
This method makes it possible to practice lapping a plurality of bars at the same time and, therefore, the efficiency of lapping increases, machining time can be shortened, and the stress applied to each of the bars spreads. However, since amount of lapping (amount of height) is controlled by the lapping time, it is not possible to change the amount of lapping by each bar to be lapped at the same time, and therefore it causes the serious problem that the characteristics of the magnetic head slider to be manufactured vary widely.
To solve the above-mentioned problem, according to the prior art, JP laid open 2001-6128 propose a method for lapping control, which is referred as resistance lapping guide (RLG), by measuring the value of resistance of sensors which are formed on the bar.
However, for the lapping by RLG method, it is required to lap only one bar fixed on one holding jig, which is mounted on one lapping apparatus, based on its principle of operation.
Therefore following problems are caused by use of RLG method.    (1) As the thin film magnetic head advances, the required characteristics become more severe, so that in the magnetic head slider manufacturing process, the yield rate is decreasing, because a lot of magnetic head sliders are rejected in the quasi static test (QST), especially rejected by bad output and asymmetry characteristics. It decreases the yield rate in the head gimbal assembly (HGA) process, in which the magnetic head sliders are attached to suspension arms.    (2) Similarly, since it is required for ABS surface to finish with high accuracy, processing becomes more difficult. Therefore profile about the finished surface of the magnetic head slider, for example recess or crown profile has varied widely. Wide variability of the profile causes the instability of magnetic spacing, such as the height thereof when airborne, to increase the variation of electromagnetic conversion transfer characteristic in the HGA process. Therefore such leads to decreasing of the yield rate in the HGA process.